Novel film compositions

ABSTRACT

Compositions useful in the manufacture of soft, heat sealable films and sheeting material of improved strength are prepared from blends of about 30 to about 80 wt. % of ethylene - methyl acrylate copolymer (EMA) and about 20 to about 70 wt. % of very low density polyethylene (VLDPE) having a density in the range between about 0.902 and about 0.910 gm/cc.

This application is a continuation of application Ser. No. 277,821,filed Nov. 30, 1988, now abandoned, which is a continuation-in-part ofapplication Ser. No. 112,344 filed Oct. 26, 1987, now abandoned which isa division of Ser. No. 855,972, filed Apr. 25, 1986, now abandoned.

BACKGROUND OF THE INVENTION

Films made from ethylene-methyl acrylate copolymers (EMA) are very soft,limp and flexible with excellent low temperature seal characteristics.They have been used for disposable gloves, medical packaging, hospitalsheeting, etc., and also in other applications such as a heat seal layerin co-extrusion.

However, the strength properties of the materials are quite low.Specifically, the low puncture resistance, impact strength and tensilestrength render the film unsuitable for many applications.

It is therefore an object of the present invention to provide a resincomposition based on EMA, which composition is suitable for themanufacture of shaped articles having improved puncture resistance, tearstrength and tensile strength, while retaining the desirable propertiesof EMA resins. It is also an object of the present invention to providean EMA based puncture resistant film of improved tear strength andtensile strength.

These and other objects will become apparent from a reading of thespecification and appended claims.

THE INVENTION

In accordance with the present invention there is provided a resincomposition consisting essentially of:

(A) from about 30 to about 80 percent by weight of an ethylene-methylacrylate copolymer (EMA) and

(B) from about 20 to about 70 percent by weight of a very low densitypolyethylene (VLDPE) having a density between about 0.902 and about0.910 gms/cc. No other resin components are present in the composition.

The preferred concentration of component (A) is between about 50 andabout 70 wt. % and that of component (B) between about 30 and about 50wt. %.

The EMA copolymer usually contains from about 17 to about 22 wt. %polymerized methyl acrylate groups. It is produced in a conventionalhigh pressure autoclave reactor by the polymerization of a mixture ofethylene and methyl acrylate. The copolymers are available commercially,e.g., the Poly-Eth® resins from Chevron Chemical Company.

The VLDPE is a linear nonpolar, nonelastomeric polymer of narrowmolecular weight distribution. It is a copolymer of ethylene and atleast one comonomer selected from C₄ to C₁₀ alphaolefins. The melt indexof the VLDPE copolymer is in the range of from 0.1 to about 10 g/10 min.The copolymer resins are commercially available, e.g., the UCAR® FLXresins from Union Carbide Corporation. It is critical that VLDPE havinga density in the required range be selected as component (B). The use ofa VLDPE resin having a density lower than 0.902 gms/cc causes thesurfaces of any articles shaped from the composition to be sticky andtacky. Similarly, an elastomeric copolymer of ethylene and at least oneC₄ and C₁₀ alphaolefin comonomer is not at all suitable as component (B)due to the incompatability of the elastomer with the EMA resin, causingmajor operational problems as well as production of films ofunacceptable quality. On the other hand, the use of a linear low densitypolyethylene (LLDPE) having a density above 0.910 gms/cc instead of theVLDPE would result in an unacceptably stiff product.

The VLDPE concentration should not exceed 70 wt. % to prevent loss ofthe excellent tactile property associated with EMA. Also, at the higherend of the concentration range the heat sealability would suffer. Atlower concentrations where the stiffness and heat sealability no longerwould be a problem, the improvements in puncture resistance, tearstrength and tensile strength would be quite insufficient to beacceptable.

The composition can, if desired, contain various additives, e.g.,antiblocking agents, slip additives, pigments and others as is known inthe art.

Thin films made from the resin composition are used with advantage inthe manufacture of disposable gloves, which are soft and pliable yetmuch stronger than conventional disposable gloves made from EMA alone.Other uses include medical packaging, inner coverings for foamedcushions or pads to be inserted into outer decorative covers, etc.

Various methods may be used for producing the film, e.g., by any of theknown tubular blowing methods or by the so called chilled roll castinqmethods. The thickness of the film can be between about 0.2 and about 2mil, and should preferably be in the range of from about 0.3 to about1.5 mil. Disposable glove film is preferably having a thickness betweenabout 0.8 and 1.2 mil.

Blown or cast thicker films or sheet material (e.g., in the range fromabout 2 to about 10 mil) made from the resin blend are used with greatadvantage in the manufacture of hypothermic pads or hospital bedcushions. These are pads made by sealing film to film to create channelsthrough which water or other heating or cooling fluids can flow (in thecase of hypothermia pads). These pads must have strong seals so they donot rupture, must be extremely soft to conform to varying body shapes,and must not be stiff creating annoying noise and rattle. The use of theEMA/VDPE films satisfy all the requirements of acceptable pads orcushions of these types.

The following examples are provided to further illustrate the invention.

EXAMPLES 1-6

The blends of Examples 1-5 were prepared with the componentconcentrations shown in Table I. The EMA resin was obtained from ChevronChemical Company under the trade name Poly-Eth® 2258. The copolymercontains about 20 wt. % polymerized methyl acrylate units and is an FDAapproved material for food packaging. The VLDPE component was UnionCarbide Corporation's DFDA® 1137 Natural 7 resin, which has FDA approvalfor food contact applications.

Films of about 1 mil thickness were blown from each of the compositionsof the examples and subjected to physical testing. The results of suchtesting are shown in Table I.

The blend of Comparative Example 6 was prepared almost identically tothe blend of Example 4, the only difference being that instead of theVLDPE component having a density of 0.906 g/cc was substituted. A blownfilm of about 1 mil thickness was prepared from the blend and subjectedto physical testing. The results are also shown in Table I for readycomparison with those of Examples 1-5. The test results show that thefilm of Comparative Example 6 containing a LLDPE of a density higherthan the maximum allowable density of the VLDPE component used in thisinvention had an unacceptable stiffness and much lower impact andtensile strength than those of the film of Example 4. Furthermore, thestiffness of the film of Example 6 is worse than that of the filmprepared from VLDPE by itself as shown by the comparison of the 1%Secant Modulus values of Examples 5 and 6. Finally, the punctureresistance or impact of the film of Example 6 is worse than that of thefilm of Example 1 prepared from EMA alone. In other words, the use ofLLDPE as a blend component instead of VLDPE does not result in filmshaving the desired softness, flexibility, and puncture resistance neededfor the intended applications.

COMPARATIVE EXAMPLES 7-8

In Comparative Example 7 and 8, the VLDPE component of Example 4 wassubstituted with two different VLDPE resins having densities below theminimum value of 0.902 gms/cc. Thus in Example 7, the VLDPE was UnionCarbide resin pellets DFDA® 1138 having a density of 0.900, whichpellets were quite tacky, while the ones in Example 8 (DFDA® 1210) had adensity of 0.890 and actually felt oily to the touch. Since the pelletswere so tacky, it was extremely difficult to incorporate them even inthe small scale laboratory equipment, and from a commercial productionstandpoint it would not be feasible to use the required equipment suchas blenders and vibratory trays for conveying the resin. In short, VLDPEresin compounds with a density of 0.90 or lower would preclude them fromlarge scale commercial use. Although the films prepared from the blendsof Comparative Examples 7 and 8 had acceptable softness, flexibility andpuncture resistance, they contained an exessive amount of gels, makingthem completely unacceptable for commercial use. The test results areshown in Table II.

                                      TABLE I                                     __________________________________________________________________________              Example                                                                       1    2    3    4    5    6                                          __________________________________________________________________________    Blend Comp.                                                                   EMA, wt. %                                                                               100  80   60  .sup.   38.sup.(1)                                                                   0  .sup.   38.sup.(1)                         VLDPE, wt. %                                                                              0   20  .sup.   38.sup.(1)                                                                  60  .sup.   95.sup.(2)                                                                   0                                        LLDPE, wt. %                                                                              0    0    0    0    0   60                                        Tensiles                                                                      Elongation:                                                                   MD, %      260  315  355  370  655  640                                       TD, %      605  600  625  685  785  735                                       Pull:                                                                         MD, psi   3250 3950 4690 5215 4780 4435                                       TD, psi   2725 2705 2715 3385 3850 2930                                       1% Secant Modulus                                                             MD, psi   7700 8400 9400 9500 15,500                                                                             16,420                                     TD, psi   9100 10,600                                                                             10,900                                                                             12,400                                                                             18,000                                                                             19,750                                     Tear                                                                          MD, grams/mil                                                                            34   28   32   32   176  193                                       TD, grams/mil                                                                            105  177  316  401  336  629                                       Spencer Impact,                                                                          867  872  839 1111 --    800                                       gms/mil                                                                       __________________________________________________________________________     .sup.(1) Remainder is 2% slip and antiblock additives.                        .sup.(2) Remainder is 5% slip and antiblock additives.                   

                  TABLE II                                                        ______________________________________                                                       Example                                                                       7        8                                                     ______________________________________                                        Blend Composition:                                                            EMA, wt. %       38.sup.(1) 38.sup.(1)                                        VLDPE, wt. %     60         60                                                VLDPE Density, gm/cc                                                                           0.900      0.890                                             Tensiles:                                                                     Elongation:                                                                   MD, %            480        590                                               TD, %            805        895                                               Pull:                                                                         MD, psi          6065       4755                                              TD, psi          2830       2955                                              1% Secant Modulus:                                                            MD, psi          7262       5491                                              TD, psi          8703       6566                                              Tear:                                                                         MD, gms/mil      27         69                                                TD, gms/mil      307        247                                               Spencer Impact,  952        964                                               gms/mil          (No Breaks)                                                                              (No Breaks)                                       ______________________________________                                         .sup.(1) Remainder is 2% slip and antiblock additives.                   

Various modifications and alterations can be made to the compositionsand films without departing from the scope of this invention, which isdefined by the specification and appended claims.

What is claimed is:
 1. A resin composition suitable for processing intofilm consisting essentially of from about 30 to about 80 wt. % of anethylene-methyl acrylate copolymer and from about 20 to about 70 wt. %of a very low density polyethylene having a density from about 0.902 toabout 0.910 gms/cm³, said very low density polyethylene being anon-elastomeric copolymer of ethylene and at least one comonomerselected from alpha-olefins containing from 4 to 10 carbon atoms, saidfilm being soft, pliable, heat sealable and having a thickness fromabout 0.1 mils to about 10 mils.
 2. The composition of claim 1 whereinthe ethylene-methyl acrylate comprises from about 17 to about 22 wt. %of polymerize methyl acrylate groups.
 3. The composition of claim 1wherein the concentration of ethylene-methyl acrylate ranges from about50 % to about 70 wt. % and the concentration of the very low densitypolyethylene ranges from about 30 to about 50 wt. %.